1. Field of the Invention:
This invention relates to a process for making a zeolite, preferably a MFI-type structure, most preferably a ZSM-5 MFI zeolite, having germanium in the framework (hereinafter referred to as “Ge-zeolite” or, if the zeolite is ZSM-5 MFI, Ge-ZSM-5). This Ge-zeolite may be synthesized with or without using fluoride compounds.
2. Description of the Prior Art:
Zeolite is a crystalline hydrated aluminosilicate that may also contain other metals, such as sodium, calcium, barium, and potassium, and that has ion exchange properties (Encarta® World English Dictionary [North American Edition] © & (P) 2001 Microsoft Corporation). A method for preparing a zeolite comprises (a) preparing an aqueous mixture of silicon oxide and sources of oxides of aluminum; and (b) maintaining said aqueous mixture under crystallization conditions until crystals of said zeolite form.
Synthetic zeolites are normally prepared by crystallization of zeolites from a supersaturated synthesis mixture. The resulting crystalline product is then dried and calcined to produce a zeolite powder. The zeolite powder may be bound for use in certain equipment and process, e.g. fluidized bed reactor.
Synthesis of a MFI-type zeolite with germanium in the framework is disclosed in “Synthesis and Characterization of Ge-ZSM-5 Zeolites, H. Kosslick et al., J. Phys. Chem., vol. 97, p. 5678–5684 (1993). Hydrofluoric acid (HF) is used in the synthesis.
U.S. Pat. No. 5,391,287 discloses a crystalline zeolite SSZ-35 prepared with a particular templating agent. In the discussion of the background, it is noted that organocations (organic amines and quaternary ammonium cations) exert influence on the zeolite crystallization process by affecting the characteristics of the synthesis gel, e.g. modifying the gel pH. SSZ-35 may contain germanium. There is no disclosure on the effect of the pH of the synthesis gel on incorporation of germanium in the zeolite framework.
U.S. Pat. No. 5,073,673 discloses a process for the production of high-octane gasoline using a crystalline aluminogallosilicate obtained by hydrothermally treating a homogeneous aqueous mixture containing a source of silica, a source of alumina and a source of gallia and having a pH of 8–13 at a temperature of 150°–250° C. with stirring until crystals of said aluminogallosilicate are formed. The particle size of the aluminogallosilicate depends on factors such as the kind of the silica source, the amount of organic additives (e.g. quaternary ammonium salt), the amount and kind of the inorganic salt to be used as a mineralizer, the amount of base in the gel, the pH of the gel, the temperature of the crystallization and the rate of stirring. By appropriately controlling these conditions, crystalline aluminogallosilicate having a particle size of about 0.05–20 micron with at least 80% by weight thereof having a particle size of 0.01–10 micron may be produced. Germanium is listed as one of over thirty auxiliary components.
U.S. Pat. No. 4,923,594 discloses a fluid catalytic cracking process with a fluid catalytic cracking catalyst of a microporous crystalline multi-compositional, multiphase composite of SAPO-37 non-zeolitic molecular sieve and a zeolitic molecular sieve. Recipes calling for pHs of 12 or higher, e.g., sodium hydroxide as a reagent, are not desirable due to decomposition of the substrate. A lower pH is obtained by using ammonium salts as substitutes for some of the caustic. The initial gel pH of the non-zeolitic molecular sieve is weakly acidic to facilitate incorporation of the hydrolyzable metal cation form of the elements into the frameworks, and inhibiting their precipitation as hydroxides or oxides. In Example 1 the pH of the zeolitic molecular sieve was initially 4.9 and raised to 7.2. Germanium is listed as one of approximately 14 elements capable of forming a framework tetrahedral oxide in the non-zeolitic molecular sieve.
It would be advantageous to have a process for making a germanium zeolite-type catalyst in which did the amount of germanium incorporated into the framework could be controlled and maximized.